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    <!-- 把行划分成 12 个格子 -->

    <!-- xs extreme small超小屏幕   sm small小屏幕 md middle中等屏幕   lg large大屏-->
    
    <!-- row只能在 container下   row下 只能放colomn -->

    <!-- 父容器的尺寸的常见划分

+ 超小屏幕（手机，小于 768px）：设置宽度为 100%
+ 小屏幕（平板，大于等于 768px）：设置宽度为 750px
+ 中等屏幕（桌面显示器，大于等于 992px）：宽度设置为 970px
+ 大屏幕（大桌面显示器，大于等于 1200px）：宽度设置为 1170px  -->
    <div class="container">
      <div class="row">
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
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        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
        <div class="col-xs-12 col-sm-6 col-md-4 col-lg-3"><div class="content"></div></div>
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    <div class="row">
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
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      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
      <div class="col-xs-4 col-sm-4 col-md-5 col-lg-1"><div class="content"></div></div>
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